This invention relates generally to a pump sprayer of the pressure build-up variety as set forth in my prior U.S. Pat. No. 4,051,983, and more particularly to such a pump sprayer as having a precise output feature.
In such pump, the pump chamber is provided at its inner end with a reduced diameter portion for the reception of a reciprocable small diameter control piston, against which the return spring exerts an upward force, so that a discharge valve carried by the control piston is urged into a seated position relative to a discharge passage extending through the main pump piston which reciprocably operates within a large diameter portion of the pump chamber. In addition to seating the discharge valve, the thrust of the return spring, transmitted through the control piston and discharge valve, serves to raise both pistons on their intake or suction stroke, following each manually applied downward or compression stroke. The pistons therefore delimit opposite ends of a dual diameter pump chamber the volume of which is varied during pumping, while relative movement between the pistons, resulting from pressure changes within the pump chamber, effects the opening and closing of the discharge valve. Thus, the pressure of the return spring maintains the discharge valve closed or seated except when the pressure of liquid in the pump chamber acting on the control piston exceeds the spring pressure required to seat the discharge valve. And, the pump is primed by the provision of a protuberance or groove in the wall of the reduced diameter pump chamber to effect reverse flow of entrapped air from the pump chamber into the liquid supply container as a piston seal on the control piston engages the protuberance or the groove.
However, experience has shown that the amount of spray discharge varies depending on the amount of external finger pressure applied during pumping, such that a relatively heavy plunger force produces a greater discharge volume compared to the discharge volume sprayed upon application of a relatively lighter plunger force. During pumping upon application of the relatively heavy plunger force, the discharge valve member on the lower control piston is caused to shift a greater distance away from the discharge valve seat during which time the discharge valve remains open for the spray dispensing of a given volume of liquid. However, upon the application of a weaker plunger force during pumping, it has been found that the discharge valve member on the control piston shifts into its open position to a lesser extent as the lower control piston moves relative to the upper main pump piston a lesser amount compared to that upon application of the stronger plunger actuating force. The discharge passage thus remains open a duration of time depending on the difference in the relative travel distance of the discharge valve during a discharge open position. This duration is longer in the presence of relatively heavily applied plunger forces and thereby accounts for a different spray output. This imprecise output is generally unacceptable for those applications of various medicants, for example, requiring metered dosage or controlled output.